1. Field of the Invention
The present invention relates to an insulated electric wire with excellent coil insertability.
2. Description of the Related Art
Motors, transformers or the like are formed by, for example inserting plural insulated electric wire coils into a stator slot, and then welding ends of the plural coils inserted to each other.
The coils are formed by high-speed coiling insulated electric wires. To reduce flaws caused in the insulated electric wire surface during the coil formation, the coils are therefore required to have an excellent coilability, i.e., an enhanced lubricity of the insulated electric wire surface.
To improve the lubricity of the insulated electric wires, it has been suggested to, for example apply to their insulating layer a resin coating with a lubricant, such as a polyethylene oxide, added to its base resin, and bake it to form a lubricating layer (insulating sheath layer). Refer to JP-A-2007-213908, for example.
Also, it has been suggested to apply to a conductor a resin coating with a stabilized isocyanate compound and a lubricant combined into its base resin, and bake it to form a lubricating layer (refer to JP-A-9-45143, for example), or apply to a conductor a resin coating with a titanate ester combined into its base resin, and bake it to form a lubricating layer (refer to JP-A-7-134912, for example).
Refer to JP-A-2007-213908, JP-A-9-45143 and JP-A-7-134912, for example.
In recent years, on the other hand, motors or transformers have been required to have a high efficiency from an energy saving point of view. To this end, the coils are inserted into the stator slot with little space left therein, to increase the ratio (fill factor) of the conductor cross-sectional area of the insulated electric wires to the stator slot cross-sectional area. Therefore, to reduce flaws caused in the insulated electric wire surface during the coil insertion, the insulated electric wires are required to have an excellent coil insertability, i.e., a reduced coil insertion force required to insert the coils into the stator slot.
However, the conventional insulated electric wires are insufficient in coil insertability. Therefore, to improve this coil insertability, a large amount of lubricant to add to the insulating coating is used, thereby leading to a cloudy coating (lubricating layer), or a poor appearance, such as a foamy, granular, rough, or hollow coating surface.